Dozens are feared to be dead after a miliary helicopter collided with an American Airlines plane near Washington, D.C.; an investigation is underway after an experienced skydiver died south of the Valley;

A major emergency operation is underway in Washington DC after an American Airlines flight collided in mid-air with a military helicopter. BBC Verify's Nick Eardley has been taking a closer look at what we know so far about the circumstances leading up to the collision.